The present invention relates generally to switching devices and, in particular, to a system including a switching device and an evaluation device for determining a remaining service life of a contact piece of the switching device.
German Patent Application No. DE 37 14 802 A1 describes an electric switch in which contact erosion is monitored via an optical fiber system. In this context, a fiber optic guide is arranged between the end face of the contact piece to be monitored and the contact carrier assigned thereto, nearly parallel to the end face of the contact piece. Because of this, unacceptably high contact erosion results in the destruction of the fiber optic guide and thus, in the change of its optical properties. These changes are then evaluated so that the existence of a certain contact erosion can be detected at a stage where the contacts can still be expected to have a limited service life. In this context, however, erosion can actually be detected only upon the destruction of the fiber optic guide and thus, only after a certain wear of the contact piece. Moreover, the contact piece to be examined is predamaged by embedding a fiber optic guide so that the contact piece experiences a suddenly occurring increase in wear due to the opening in the material when it is eroded down to the level of the fiber optic guide.
An object of the present invention is to provide a system capable of evaluating, in a nearly wear-free manner and without predamaging the contact piece, contact piece wear at any arbitrary instant of the contact piece wear.
The present invention provides a system including a switching device, a sound device and an evaluation device. The switching device includes a housing and a contact system disposed in the housing, the contact system including a contact piece carrier and a contact piece disposed on the contact piece carrier. Th e sound device produces and captures structure-borne sound waves so as to determine an equivalent criterion useable for determining a remaining service life of the contact piece. The evaluation device evaluates the equivalent criterion.
Each state of wear of a contact piece is associated with specific characteristics thereof. Thus, as the wear increases, the contact piece changes its properties with respect to the transmission or reflection characteristics for sound waves passing through the contact piece. According to the present invention, these changes are detected by acoustic aids and evaluated in an evaluation device, thus determining a corresponding wear state. According to the present invention, acoustic aids are used which, on one hand, are capable of producing sound waves in a desired degree so that a defined injection of sound waves can be injected into the contact piece to be examined and which, on the other hand, are able to capture sound waves which occur in the contact piece.
Advantageously, a single acoustic aid in the form of a piezoelectric element may be used for producing and capturing the sound waves. These high-power piezoelectric elements can be arranged, in particular, in the form of thin layer elements on the contact piece carrier, preferably immediately opposite the contact piece to be examined, on the other side of the same contact piece carrier.